CIVL 1100 Discovering Civil and Environmental Engineering

Unit 10. Foundations for High-rise Buildings

Professor Limin Zhang, PhD, FASCE

Department of Civil and Environmental Engineering

The Hong Kong University of Science and Technology

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• Types of foundations

• Design requirements

• Layout of foundations for high-rise buildings

• Geotechnical lab session

Hong Kong ranks first in the world in both skyscraper and

high-rise count, with at least 52 skyscrapers over the height

of 200 m, and more than 7,687 highrise buildings. A high-

rise is defined as a structure at least 35 m or 12 stories tall.

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Amazing Buildings Around the World

Chicago Spiral CCTV Beijing

Beijing Olympic Stadium Shanghai World Financial Center

(492m) Dubai Rotating Tower

The Nest, Beijing

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Every single building must be supported on a solid foundation. Types of foundations? Design requirements?

Common layout of foundations for high-rise buildings?

828 m (2,716 ft)

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Types of Foundations

• Foundation

– As a structural member that connects the superstructure with the ground

– As a system member transferring loads to soils/rocks

• Foundation types

– Shallow foundations

– Deep foundations

– Offshore foundations

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Shallow Foundations

• Square

• Rectangular

• Circular

• Continuous

• Combined

• Ring

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Shallow Foundations

HKUST Enterprise Center

Shallow foundations, where applicable, are often the most economic.

Shallow Foundations

HKUST 10-story student hostel

HKUST Enterprise Center

Eiffel Tower Each of the four legs of

Eiffel Tower is supported

by a footing. Once the

tallest structure in the

world (1889), its

foundation has not

experienced any

excessive settlement.

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Deep Foundations

Electricity Transmission towers (due to wind and broken cable)

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Shaft

friction fs

Toe resistance qb

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Deep Foundations – Driven Piles

• Prefabricated members driven into ground

Deep Foundations - Jacked Piles

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Deep Foundations – Bored Piles/Drilled Shafts

• Drill cylindrical hole, install reinforcement cage, and pour concrete

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Bored Pile Construction: Flight Auger

Bored Pile Construction: Grab and Chisel

2.3 m diameter casing and grab

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Bored Pile Construction: Drilling in Rocks

A 2.3 m diameter drill bit

Bored Piles in Rocks: Bellout of Pile Toe

D D

< 1.5D

< 30

Without bellout With bellout, 1.5D

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qb = 5–10 MPa

Soil

Bedrock

fs

The shaft resistance in soil layers

is often ignored in Hong Kong,

but is the primary resistance for

piles when bedrock cannot be

reached.

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Bored Piles: Reinforcement Cage

Offshore Foundations vs. Water Depth

Subsea wellhead

Pipeline

Risers

Anchors

Vertical

risers

Jacket

Wellheads

Manifold

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Offshore Piles for Wind Turbines

Gravity

base, water

depth < 25m

Monopile, water

depth < 35 m

Jacket

structure Floating

platform

Foundations used to support offshore wind turbines. The

cost of foundations can represent up to 50% of the

development cost for an offshore wind farm.

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• Types of foundations

• Design requirements

• Layout of foundations for high-rise buildings

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Performance Requirements

• Strength requirements • Geotechnical strength: the ability of the soil or rock to accept the

loads imparted by the foundation without failing (bearing failure)

• Structural strength: the foundation’s structural integrity and its ability to safely carry the applied loads

• Serviceability requirements

• Both total settlement and differential settlement must be smaller than their allowable values

• Constructability requirements

• The foundation must be designed such that a contractor can build it without having to use extraordinary methods or equipment

• Economic requirements

• Economic, but more conservative than superstructures

Consequences of failure (to future engineers like you?)

If a builder builds a house for a man and does not make its construction firm, and the house he has built collapses and causes the death of the owner of the house, that builder shall be

put to death.

From The Code of Hammurabi, Babylon, CIRCA 2000 B.C.

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Building collapse in Shanghai due to foundation failure, 5:30 am, 27 June 2009 Photocredit: Pei Xing

Short Pile Scandal at Shatin, 1999

• 21 of the 36 large diameter bored piles were 2-15 m shorter than required

• 11 were founded in soil instead of bedrock

• The two buildings were demolished in 2000 when constructed up to 33rd and 34th floors.

• Total loss: HK$605 million

發現地基短樁的圓洲角愉翠苑，其中兩幢居屋大樓D及E座，經勘測後發現九成樁柱不合標準，短樁更集中在同一邊，令兩幢大樓出現傾斜；房委會決定拆卸這兩幢已興建至三十四層高的居屋。

http://ihouse.hkedcity.net/~hm1203/li

nks/hk-yu-chui.htm

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• Short piles found in 1999 • Foundation retrofitted • Over HK$100 million for maintenance • Vacant for 13 years, sold in 2013 • Loss of over HK$500 million +

reputation

天頌苑兩幢大廈在九九年被揭發出現短樁問題，房署其後斥資一億五千萬元為兩幢大廈進行加固地基工程，當年房委會亦要賠償訂金和利息開支予有關居屋的準買家，以及承擔一千二百八十個單位延遲出售的損失，加上七千萬元的訴訟費，涉及的金額高達六億二千多萬元，但房署早前只獲保險公司賠償兩億多元，因此事件令房署損失四億多元。

The Sun, 25 Jan. 2007

房委會推出這批居屋貨尾單位，主要集中於當年爆出短樁醜聞的天水圍天頌苑的兩幢居屋，事隔至今已十多年，房委會一直未有推售這批單位. 東方電視, 5 Feb. 2013

5 Feb. 2013

Short Pile Scandal at Tin Shui Wai, 1999

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Limit States

A limit state is a condition beyond which a structural component ceases to fulfill the function for which it is designed.

• Strength limit states (ultimate limit states)

Geotechnical resistance

Structural resistance

• Service limit states (function of structure under expected

service loads)

Deformations, vibration, cracking, local damage, deterioration

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Some Ultimate Limit States for Foundations

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Modes of Building Settlement

(a) Uniform

(b) Tilting without distortion

(c) Distortion

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Global Factor of Safety

Geotechnical resistance Deformation

Rn = Ultimate bearing capacity

FS = Factor of safety

Qi = Nominal load effect

di = Estimated displacement under the nominal service load effect

dn = Tolerable displacement

ni dd

in Q

FS

R

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Recommended Factor of Safety

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Allowable toe resistance of piles on rock (Code of Practice for Foundations 2004)

Greater design values acceptable if verified by load tests.

Piles can be founded in soils if with proper justifications.

Example: Capacity of Bored Piles on Rock

D D

≤ 1.5D

Without bellout

qult = 10 MPa

With bellout, 1.5D

qult = 10 MPa

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Quiz

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Which of the following is NOT one of the basic requirements for designing a proper foundation? A. Strength B. Founding on bedrock C. Constructability D. Serviceability

In the Shatin short pile scandal, what was the major reason that threatened the safety of the buildings concerned? A. The pile diameter was too small to take the load B. The pile material was too weak to provide adequate strength C. The piles had not reached the bedrock to provide enough bearing capacity D. The design requirements were too high to achieve

Damage due to Differential Settlement

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Tolerable Foundation Settlement for Structures on Sand (Eurocode 1, 1993)

Total settlement

Isolated foundation 25 mm

Raft foundation 50 mm

Differential settlement between adjacent columns

Open frames 20 mm

Frames with flexible cladding or finishes 10 mm

Frame with rigid cladding or finishes 5 mm

Relative rotation (angular distortion) 1 / 500

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Allowable Post-construction Settlement for High-speed

Railways (Chinese Ministry of Railways 2007)

New passenger train, design speed (km/h)

General roadbed

(mm)

Bridge approach

(mm)

200-250 100 50

250-300 50 20

300-350 15 5

Roadbed

Subbase II

Subbase I

Ballast

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The Leaning Tower of Pisa project

1173-1178: 19.6 m diameter ring-shape footing & 3.5-story tower. Tilting started.

1360-1370: constructed to the belfry, about 56 m tall, tilting 3° toward south

1838: 2.5 m settlement. Construction of the trench (to see the beautiful carvings) added 0.5 m settlement.

End of 20th century: 5.5 ° tilting, top 5.2 m off plumb.

1997-2001: soil extraction, back to 5°.

Correcting the Tower Using Soil Extraction

Soil extraction (1997-2001): Back to 5.0.

There was no intention to correct the tower to perfectly vertical.

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• Types of foundations

• Design requirements

• Layout of foundations for high-rise buildings

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International Commerce Center 2002-2010

• 118 floors, 484 m above ground

• 241 closely spaced shaft-grouted friction barrettes

• Founding level: – 60 mPD to -96 mPD

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Foundation for International Commerce Center

Caisson Load (MN) D D + L +/- W

Bell-out Diameter (m)

AA BB DD EE

327 277 180 142

380 322 209 164

131 93 98 79

10.5 9.5 8.2 7.2

Bank of China Tower

Grouting

Diaphragm wall

Caisson

Main column

Drainage

Basement

Wall

72 story /369 m high

Grouting

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1985-1990

The Center used four 24 m diameter caissons of an average depth of 45 m

as the principal foundation.

The Centre

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1995-1998

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Shanghai Jinmao Tower 1994-1999

• 88 story /360 (420) m high • Clay /silt • 429 driven steel tube piles, d=914 mm, t =20

mm, L=83 m

The Shanghai World Financial Center (left)

and the Jin Mao Tower (right)

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Taipei 101 508 m high 1999-2004

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Taipei 101: Evenly Distributed Bored Piles

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18

17

16

15

14

13

12

7

9

10

11

8

5

6

4

3

A

1.6

2

1

B C D KGE F H.5H J L M N P Q SR T

• Tower – 380 bored piles

– 1.5 m diameter

– 62 – 81 m length

– Socket into bedrock

– 15 – 33 m (Avg. 23 m)

• Podium – 167 bored piles

– 2.0 m diameter

– 57 – 81 m length

– Socket into bedrock

– 5 -29 m (Avg. 15 m)

Podium

Tower

Burj Khalifa, Dubai 2004-2010

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Tower area • 196 bored piles • D = 1.5 m, L = 47.45 m • Raft at -7.55 m, thickness = 3.7 m

Podium Area • D = 0.9 m, L = 30 m • Raft at -4.85 m, thickness = 3.7 m

Height: 828 m

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Introduction to the Geotechnical Engineering Laboratory Session

Building collapse due to liquefaction in 1964 Niigata earthquake

In 1971, the upstream of the lower San Fernando dam in California failed about a minute after the end of an earthquake, an interesting punctuation mark to the liquefaction debate at that time.

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Soil Liquefaction

• A phenomenon where a saturated soil substantially loses its strength and stiffness in response to an applied shear stress, usually earthquake shaking, causing it to behave like a liquid.

• The phenomenon is most often observed in saturated, loose sandy soils.

Sand boils in liquefaction

Your Geotechnical Laboratory: Laboratory Soil Liquefaction Tests

• Prepare saturated sand beds of different densities

• Shake the sand beds at different intensities

• Observe soil liquefaction

Water table

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Test Objectives

• To gain insight into soil liquefaction and to identify the key factors that influence soil liquefaction

Frequency

Shaking intensity

Duration

Water content

Soil density

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Geotechnical Lab Session

Refer to “Lab Groups and Name Lists for Geotechnical

Engineering Experiments”

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Week Date Time Session Group

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17 Nov 2015 13:00-14:50 LA 3 C1-C4

17:00-18:50 LA 2 B1-B4

19 Nov 2015 9:00-10:50 LA 4 D1-D4

13:00-14:50 LA 1 A1-A4

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24 Nov 2015 13:00-14:50 LA 3 C5-C8

17:00-18:50 LA 2 B5-B8

26 Nov 2015 9:00-10:50 LA 4 D5-D8

13:00-14:50 LA 1 A5-A8

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Thank you!